lockf - apply, test or remove a POSIX lock on an open file
SYNOPSIS
#include <sys/file.h>
int lockf(int fd, int cmd, off_t len);
DESCRIPTION
Apply, test or remove a POSIX lock on an open file. The
file is specified by fd. This call is just an interface
for fcntl(2). Valid operations are given below:
F_LOCK Set an exclusive lock to the file. Only
one process may hold an exclusive lock
for a given file at a given time. If the
file is already locked it blocks until
the previous lock is released.
F_TLOCK Same as F_LOCK but never blocks and
return error instead if the file is
already locked.
F_ULOCK Unlock the file.
F_TEST Test the lock: return 0 if fd is unlocked
or locked by this process; return -1, set
errno to EACCES, if another process holds
the lock.
RETURN VALUE
On success, zero is returned. On error, -1 is returned,
and errno is set appropriately.
ERRORS
EAGAIN The file is locked and the LOCK_NB flag was
selected, or operation is prohibited because the
file has been memory-mapped by another process.
EBADF fd is not an open file descriptor.
EDEADLK
Specified lock operation would cause a deadlock.
EINVAL An invalid operation was specified in fd.
ENOLCK Too many segment locks open, lock table is full.
CONFORMING TO
SYSV
fcntl(2), flock(2)
There are also locks.txt and mandatory.txt in
/usr/src/linux/Documentation.
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